It is known in the art that alpha-olefins can be polymerized in the presence of catalytic systems containing solid TiCl.sub.3 or solid TiCl.sub.3 mixed with or cocrystallized with solid metallic halides and activated by an organic compound of aluminum.
These solid compositions containing titanium trichloride can be prepared by a number of different processes. One of these processes is the reduction of TiCl.sub.4 by hydrogen. Another process consists of reducing TiCl.sub.4 with a metal such as aluminum obtaining titanium trichloride cocrystallized with aluminum chloride. Another process preferred for several reasons is reduction of TiCl.sub.4 with alkyl aluminum (halides). The TiCl.sub.3 product then obtained is normally in the brown beta form and contains either aluminum chloride or alkyl aluminum chloride by-products, or both, associated with the TiCl.sub.3. For optimum catalytic effects, it is preferred that this brown material be converted to the purple form by either heating or using excess titanium tetrachloride.
When alpha-olefins, for example propylene, are polymerized with these catalysts, commercially undesirable amounts of amorphous polypropylene is formed along with the desirable isotactic crystalline polypropylene. It is well known in the art that third components can be added as complexing agents to titanium trichloride catalysts to improve isotacticity of the crystalline polyolefins, although usually at the cost of reduced efficiency of the polymerization reaction.
Thus, Boor & Jordan have described how titanium trichloride can be improved by the addition of Lewis bases (J. Boor, Jr., "Active Site in Ziegler Catalysts", page 115 in "Macromolecular Reviews, Vol. 2"; see also D. O. Jordan, "Ziegler Natta Polymerization" in "The Stereochemistry of Macromolecules, Vol. 1", edited by A. D. Ketley, 1967, Marcel Decker Inc.).
Grignard reagents comprising magnesium compounds complexed with ethers have been used to reduce TiCl.sub.4 to TiCl.sub.3 for ethylene polymerizations. See U.S. Pat. No. 3,801,558. But the ethers are only used to solubilize the Grignard reagent which is otherwise hydrocarbon-insoluble.
That TiCl.sub.3 catalysts can be improved by the addition of Lewis bases, for example ethers, and/or TiCl.sub.4 treatments have been disclosed by Solvay et Cie, in German patent DT-2213086 (10-5-72). Solvay et Cie demonstrated in that patent how TiCl.sub.4 can be reduced with diethyl aluminum chloride to yield a brown reduction product containing titanium trichloride. This brown reduction product separated from the reaction medium was subsequently treated with a special ether, and subsequent to the ether treatment the reaction product was separated and then treated with excess titanium tetrachloride to form a purple catalyst, which when separated from the reaction medium could be activated with diethyl aluminum chloride to yield a catalyst active for the stereospecific polymerization of propylene.
Thus it is well known that Lewis bases, and specifically ethers, can be used to treat preformed catalysts to improve the stereospecificity and the activity of said catalysts. Nevertheless, carrying out the reduction step for reducing TiCl.sub.4 to TiCl.sub.3 in the presence of an aluminum alkyl Lewis base complex has not been reported nor is it obvious.